131
AGUS76 KRSA 122041
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
1240 PM PST Wed Nov 12 2025

...WIDESPREAD MODERATE TO HEAVY PRECIP LATER TODAY THRU SAT DUE TO A
LARGE LOW CARRYING TROPICAL MOISTURE INTO THE REGION...
...T-STORMS FOR PARTS OF NRN/CNTRL CA TOMORROW AND SRN CA FRI...

.METEOROLOGICAL CONDITIONS (WED PM - TUE AM)...

Observations show a few hundredths of an inch or so far parts of the
nrn CA coast over the past 6 hours as tropical moisture begins to
arrive. The main event will come later today through Saturday as the
elongated trough offshore breaks off into a closed low sending a
tropical moisture wrapped cold front through CA for tomorrow/Friday.
Expect widespread moderate to locally heavy rainfall and occasional
thunderstorms. As the front moves through, the low will travel
southward just offshore of the coast before what`s left of it moves
inland through srn CA over the weekend. Little has changed since
this morning, models continue to disagree on the
timing/positioning/movement of this system over the next few days as
do the ensembles all along parent det model lines. QPF clusters for
12z Thurs to 12z Fri are split into 3 groupings each dominated by
members from either the CMC (80% in cluster 3), the ECMWF (92% in
cluster 1), or the GFS (83% in cluster 2). The points of
disagreement remain how much heavy precip to spread across the
Sierra, the Russian, and down the valleys/coastal srn CA in addition
to overall timing/positioning of the system. The det runs have not
come much closer to agreeing on these points either which is leading
to the same disagreements in QPF in the same time frames mentioned
in the morning discussion. There continues to be hinting of an
additional system after this one early next week, but uncertainty is
still high.

Due to this uncertainty, did not elect to make huge changes to the
QPF. Blended in the latest NBM in some instances while also
consulting the 12z GFS/ECMWF. This lead to changes on the order of
0.10-0.50" either up or down depending on location for tonight
through late Sunday afternoon. There is potential for a good deal
more QPF over coastal srn CA, but timing issues and differences in
where the low will be at the time that area will experience the
tropical moisture mean low confidence for now. If the low sets up in
the right (or wrong depending on your view) spot, favorable
southwest flow into the Transverse could bring up the numbers quite
a bit. QPF 00z Thurs-00z Mon: 2.50-4.50" across the Sierra/central
coast mountains (locally higher Big Sur), 2.50-5.50" Shasta, 4-
6.50+" Transverse, 2-4" coastal srn CA, 1-2.50" Bay Area/central
coast/valleys, and 0.75-1.50" north coast. For early next week (00z
Mon-12z Tues), predicting another 0.50-1" across the Sierra, 0.25-
0.75+" for coastal srn CA (up to 1" or so Transverse), and 0.10-
0.50"+ across most of the rest of the state.

The main system looks to be relatively warm as well with freezing
levels only bottoming out across the Sierra down to ~8 to 10.5 kft n
to s on Friday and otherwise generally staying above 10 kft before
the upper low moves inland over the weekend.

QPF graphics are available at www.cnrfc.noaa.gov/qpf.php



AS

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